Analysis and Development of a Speed Controller for Induction Motors Using a Pulse Width Modulated AC Chopper.

Abstract

AC motors have speed control capabilities only when operating from variable frequency sources, and speed control is achieved by varying the applied voltage and/or the frequency of its inversion. The speed of an induction motor may be varied by phase angle control of the stator voltage. The phase angle control method uses a thyristor and requires that the silicon controlled rectifier be fired only once in each half cycle of the applied voltage. It is perhaps, by far, the most cost effective method of speed control and may be used on all types of loads. However, the sudden switching part-way into the applied voltage every 1/100th of a second (for 50 Hz power), results in large amounts of electrical noise which generates winding losses as heat and interferes with electronic equipment. This paper presents a speed controller scheme that uses a pulse width modulated AC Chopper in parallel with an SCR to provide some average level of voltage before the thyristor is fired. The aim is to reduce or eliminate the challenges associated with the existing speed control methods. The proposed circuit was designed, then simulated using Multisim 10.14 software. Test results shows that the performance analysis carried out on the designed circuit was satisfactory.

Index Terms— AC chopper, Electronic Switch, Phase angle firing, Silicon controlled rectifier.